Optimization of Al _<b>2</b> O _<b>3</b> nanoparticles concentration to improve the tribological and rheological performance of CK4 10W-30 engine oil

This study developed and evaluated Al2O3​ nanoparticle-based nanolubricants using CK4 10W-30 engine oil as the base lubricant to improve their thermal and tribological performance. Al2O3​ nanoparticles (0.25–0.75 wt%) were dispersed in the base oil through magnetic stirring, ultrasonication, and high-pressure homogenization. Material characterized using TGA, FTIR, and XRD confirmed the thermal stability and purity of the nanoparticles, while UV–Vis spectroscopy and zeta potential analysis verified stable and homogeneous dispersion, with 0.50 wt% showing optimum stability. Thermophysical analysis revealed slight reductions in viscosity and density after the addition of nanoparticles up to a certain proportion, and 0.50 wt% was optimal, improving the rheological behavior and oil flow characteristics. The flash and fire points also increased, indicating enhanced thermal resistance. Tribological performance was evaluated using a pin-on-disc tribometer under different loading conditions (40, 50, 60, and 70 N) and rotational speeds (1200, 1400, 1600, and 1800 rpm). The results showed significant reductions in the friction coefficient and wear rate compared to the base oil, with 0.50 wt% Al2O3​ nanoparticles providing the best anti-friction and anti-wear performance. These improvements are mainly attributed to the formation of a protective nanolubricating film at the sliding interface. The developed Al2O3​-based nanolubricants demonstrate strong potential for enhancing engine performance, reducing fuel consumption, and supporting fuel-efficient and sustainable internal combustion engine operation.